Control and Data Signaling in Heterogeneous Wireless Communication Networks

ABSTRACT

A method in a wireless communication device including receiving control signaling from a base station in a control region of a downlink carrier spanning a first bandwidth, receiving a signaling message from the base station indicating a second bandwidth, receiving a first control message within the control region using a first Downlink Control Information (DCI) format size, the first DCI format size based on the first bandwidth, and receiving a second control message within the control region using a second DCI format size, the second DCI format size based on the second bandwidth, wherein the second bandwidth is distinct from the first bandwidth and the first and second control messages indicate downlink resource assignments for the downlink carrier.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a non-provisional application of co-pendingU.S. Provisional Application No. 61/220,556 filed on 25 Jun. 2009, thecontents of which are hereby incorporated by reference and from whichbenefits are claimed under 35 U.S.C. 119.

FIELD OF DISCLOSURE

The present disclosure relates generally to wireless communicationssystems and, more specifically, to the management of interference amongthe uncoordinated deployment of closed subscriber group (CSG) cells orhome eNode Bs within a wireless network of base stations or macro eNodeBs.

BACKGROUND

Some wireless communication networks are proprietary while others aredeployed in conformity with one or more standards and accommodateequipment manufactured by various vendors. One such standards-basednetwork is the Universal Mobile Telecommunications System (UMTS)standardized by the Third Generation Partnership Project (3GPP), whichis a collaboration of groups of telecommunications associations thatgenerate globally applicable mobile phone system specifications withinthe scope of the International Mobile Telecommunications-2000 project ofthe International Telecommunication Union (ITU). Efforts are currentlyunderway to develop an evolved UMTS standard, which is typicallyreferred to as UMTS Long Term Evolution (LTE) or Evolved UMTSTerrestrial Radio Access (E-UTRA).

According to Release 8 of the E-UTRA or LTE standard or specification,downlink communications from a base station (referred to as an “enhancedNode-B” or simply “eNB”) to a wireless communication device (referred toas “user equipment” or “UE”) utilize orthogonal frequency divisionmultiplexing (OFDM). In OFDM, orthogonal subcarriers are modulated witha digital stream, which may include data, control information, or otherinformation, to form a set of OFDM symbols. The subcarriers may becontiguous or non-contiguous and the downlink data modulation may beperformed using quadrature phase shift-keying (QPSK), 16-ary quadratureamplitude modulation (16QAM) or 64QAM. The OFDM symbols are configuredinto a downlink sub frame for transmission from the base station. EachOFDM symbol has a time duration and is associated with a cyclic prefix(CP). A cyclic prefix is essentially a guard period between successiveOFDM symbols in a sub frame. According to the E-UTRA specification, anormal cyclic prefix is about five (5) microseconds and an extendedcyclic prefix is about 16.67 microseconds. Data from the serving basestation is transmitted on physical downlink shared channel (PDSCH) andcontrol information is signaled on a physical downlink control channel(PDCCH).

In contrast to the downlink, uplink communications from the UE to theeNB utilize single-carrier frequency division multiple access (SC-FDMA)according to the E-UTRA standard. In SC-FDMA, block transmission of QAMdata symbols is performed by a first discrete Fourier transform(DFT)-spreading (or precoding) followed by subcarrier mapping to aconventional OFDM modulator. The use of DFT precoding allows a moderatecubic metric/peak-to-average power ratio (PAPR) leading to reduced cost,size and power consumption of the UE power amplifier. In accordance withSC-FDMA, each subcarrier used for uplink transmission includesinformation for all the transmitted modulated signals, with the inputdata stream being spread over them. The data transmission in the uplinkis controlled by the eNB, involving transmission of scheduling grants(and scheduling information) sent via downlink control channels.Scheduling grants for uplink transmissions are provided by the eNB onthe downlink and include, among other things, a resource allocation(e.g., a resource block size per one millisecond (ms) interval) and anidentification of the modulation to be used for the uplinktransmissions. With the addition of higher-order modulation and adaptivemodulation and coding (AMC), large spectral efficiency is possible byscheduling users with favorable channel conditions. The UE transmitsdata on the physical uplink shared channel (PUSCH). The physical controlinformation is transmitted by the UE on the physical uplink controlchannel (PUCCH).

E-UTRA systems also facilitate the use of multiple input and multipleoutput (MIMO) antenna systems on the downlink to increase capacity. Asis known, MIMO antenna systems are employed at the eNB through use ofmultiple transmit antennas and at the UE through use of multiple receiveantennas. A UE may rely on a pilot or reference symbol (RS) sent fromthe eNB for channel estimation, subsequent data demodulation, and linkquality measurement for reporting. The link quality measurements forfeedback may include such spatial parameters as rank indicator or thenumber of data streams sent on the same resources, precoding matrixindex (PMI), and coding parameters, such as a modulation and codingscheme (MCS) or a channel quality indicator (CQI). For example, if a UEdetermines that the link can support a rank greater than one, it mayreport multiple CQI values (e.g., two CQI values when rank=2). Further,the link quality measurements may be reported on a periodic or aperiodicbasis, as instructed by an eNB, in one of the supported feedback modes.The reports may include wideband or subband frequency selectiveinformation of the parameters. The eNB may use the rank information, theCQI, and other parameters, such as uplink quality information, to servethe UE on the uplink and downlink channels.

In the context of the Release-8 specification of Long Term Evolution(LTE) system developed by third generation partnership project (3GPP)that is based on Orthogonal Frequency Division Multiplexing (OFDM) fordownlink transmissions, the eNB-to-UE link consists of typically 1-3OFDM symbols (length is signaled via the physical control formatindicator channel (PCFICH)) at the beginning of each 1-ms sub-frame forcontrol channel, i.e., PDCCH, transmissions. Typically an OFDM symbolcomprises of an integer number of time units (or samples), where a timeunit denotes a fundamental reference time duration. For example, in LTE,the time unit corresponds to 1/(15000×2048) seconds. Thus, the PDCCHtransmissions are a first control region with a fixed starting location(contemporaneously) at the first OFDM symbol in a sub-frame. All theremaining symbols in a sub-frame after the PDCCH are typically fordata-carrying traffic, i.e., PDSCH, assigned in multiples of ResourceBlocks (RBs). Typically, an RB comprises of a set of subcarriers and aset of OFDM symbols. The smallest resource unit for transmissions isdenoted a resource element which is given by the smallest time-frequencyresource unit (one subcarrier by one OFDM symbol). For example, an RBmay contain 12 subcarriers (with a subcarrier separation of 15 kHz) with14 OFDM symbols with some subcarriers being assigned as pilot symbols,etc. Typically, the 1 ms sub-frame is divided into two slots, each of0.5 ms. The RB is sometimes defined in terms of one or ore more slotsrather than sub-frames. According to the Release-8 specification, theuplink communication between the UE and eNB is based on Single-CarrierFrequency Division Multiple Access (SC-FDMA), which is also referred toas Discrete Fourier Transform (DFT)-spread OFDM. It is also possible tohave non-contiguous uplink allocations by send uplink controlinformation and uplink data on non-contiguous subcarriers. A virtualresource block is a resource block whose subcarriers are distributed(i.e., non-contiguous) in frequency, whereas a localized RB is an RBwhose subcarriers are contiguous in frequency. Virtual RB may haveimproved performance due to frequency diversity. Release-8 UEs typicallyshare resources in the frequency domain (i.e., on an RB-level or inmultiples of an RB) rather than in time in any individual sub-frame onthe downlink.

The PDCCH contains control information about the downlink controlinformation (DCI) formats or scheduling messages, which inform the UE ofthe modulation and coding scheme, transport block size and location,precoding information, hybrid-ARQ information, UE Identifier, etc. thatis required to decode the downlink data transmissions. This controlinformation is protected by channel coding (typically, acyclic-redundancy check (CRC) code for error detection and convolutionalencoding for error correction) and the resulting encoded bits are mappedon the time-frequency resources. For example, in LTE Rel-8, thesetime-frequency resources occupy the first several OFDM symbols in asub-frame. A group of four Resource Elements is termed as a ResourceElement Group (REG). Nine REGs comprise a Control Channel Element (CCE).The encoded bits are typically mapped onto either 1 CCE, 2 CCEs, 4 CCEsor 8 CCEs. These four are typically referred to as aggregation levels 1,2, 4 and 8. The UE searches the different hypotheses (i.e., hypotheseson the aggregation level, DCI Format size, etc) by attempting to decodethe transmission based on allowable configurations. This processing isreferred to as blind decoding. To limit the number of configurationsrequired for blind decoding, the number of hypotheses is limited. Forexample, the UE does blind decoding using the starting CCE locations asthose allowed for the particular UE. This is done by the so-calledUE-specific search space, which is a search space defined for theparticular UE (typically configured during initial setup of a radio linkand also modified using RRC message). Similarly a common search space isalso defined that is valid for all UEs and might be used to schedulebroadcast downlink information like Paging, or Random access response,or other purposes.

The control messages are typically encoded using convolutional encoders.The control region includes a Physical Hybrid ARQ Indicator channel orthe PHICH that is used to transmit hybrid ARQ acknowledgments.

Each communication device searches the control region in each subframefor control channels (PDCCHs) with different downlink control indicator(DCI) formats using blind detection, where the PDCCH CRC is scrambledwith either a communication device's C-RNTI (UEID) if it is forscheduling data on the Physical Downlink Shared Channel (PDSCH) orPhysical Uplink Shared Channel (PUSCH) or scrambled with SI-RNTI,P-RNTI, or RA-RNTI if it is for scheduling broadcast control (systeminformation, paging, or random access response respectively). Otherscrambling types include joint power control, semi-persistent scheduling(SPS), and a temporary C-RNTI for use with scheduling some random accessmessages.

A particular user equipment must locate the control channel elementscorresponding to each PDCCH candidate it is to monitor (blindly decodefor each subframe control region). The CRC of each PDCCH will be maskedby a unique identifier corresponding to the user equipment that the baseunit is trying to schedule. The unique identifier is assigned to the UEby its serving base unit. This identifier is known as a radio networktemporary identifier (RNTI) and the one normally assigned to each UE atcall admission is the cell RNTI or C-RNTI. A UE may also be assigned asemi-persistent-scheduling C-RNTI (SPS C-RNTI) or a temporary C-RNTI(TC-RNTI). When a UE decodes a PDCCH it must apply its C-RNTI in theform of a mask to the PDCCH CRC for successful PDCCH decoding to occur.When a UE successfully decodes a PDCCH of a particular DCI format typeit will use the control information from the decoded PDCCH to determine,for example, the resource allocation, Hybrid ARQ information, and powercontrol information for the corresponding scheduled downlink or uplinkdata transmission. The legacy DCI format type 0 is used for schedulinguplink data transmissions on the Physical Uplink Shared Channel (PUSCH)and DCI format type 1A is used for scheduling downlink datatransmissions on the Physical Downlink Shared Channel (PDSCH). Other DCIformat types are also used for scheduling PDSCH transmissions includingDCI format 1, 1B, 1D, 2, 2A each corresponding to a differenttransmission mode (e.g., single antenna transmissions, single user openloop MIMO, multi-user MIMO, single user close loop MIMO, rank-1precoding). Also there are legacy DCI format 3 and 3A for scheduling thetransmission of joint power control information. PDCCH DCI format 0, 1A,3, and 3A all have the same size payload and hence the same coding rate.So only one blind decoding is required for all of 0, 1A, 3, 3A per PDCCHcandidate. The CRC is then masked with C-RNTI to determine if the PDCCHwas DCI format type 0 or 1A and a different RNTI if it is 3 or 3A. DCIformat type 0 and 1A are distinguished by DCI type bit in the PDCCHpayload itself (i.e. part of the control information on one of thecontrol information fields). A UE is always required to search for allof DCI formats 0, 1A at each PDCCH candidate location in the UE specificsearch spaces. There are four UE specific search spaces for aggregationlevels 1, 2, 4 and 8. Only one of the DCI format types 1, 1B, 1D, 2, or2A is assigned at a time to a UE such that a UE only needs to do oneadditional blind decoding per PDCCH candidate location in the UEspecific search space besides the one blind decoding needed for the 0,1A DCI types. The PDCCH candidate locations are the same for the DCIformat types when they are located in the UE specific search spaces.There are also two 16 CCE common search spaces of aggregation level 4and 8 respectively that are logically and sometimes physically (whenthere are 32 or more control channel elements) adjacent to the UEspecific search spaces. In the common search spaces a UE monitors DCItypes 0, 1A, 3, and 3A as well as DCI format type 1C. DCI format type 1Cis used for scheduling broadcast control which includes paging, randomaccess response, and system information block transmissions. DCI 1A mayalso be used for broadcast control in the common search spaces. DCI 0and 1A are also used for scheduling PUSCH and PDSCH in common searchspaces. A UE is required to perform up to 4 blind decodings in the L=4common search space and 2 blind decodings in the L=8 common search spacefor DCI formats 0,1A, 3, and 3A and the same number again for DCI 1Csince DCI 1C is not the same size as DCI 0,1A,3 and 3A. A UE is requiredto perform (6, 6, 2, 2) blind decodings for L=(1, 2, 4, 8) UE specificsearch spaces respectively where L refers to the aggregation level ofthe search space. The total maximum number of blind decoding attempts aUE is then require to perform per subframe control region is therefore44 (=2×(6,6,2,2)+2×(4,2)). A hashing function is used by the servingbase unit and the UE to find the PDCCH candidate locations in eachsearch space. The hashing function is based on the UE C-RNTI (orsometimes the TC-RNTI), aggregation level (L), the total number of CCEsavailable in the control region (Ncce), the subframe number or index,and the maximum number of PDCCH candidates for the search space.

Home-basestations or femto-cells are referred to as Home-eNBs (HeNBs) inthe present disclosure. A HeNB can either belong to a closed subscribergroup (CSG) or can be an open-access cell. A CSG is set of one or morecells that allow access to only certain a group of subscribers. HeNBdeployments where at least a part of the deployed bandwidth (BW) isshared with macro-cells are considered to be high-risk scenarios from aninterference point-of-view. When UEs connected to a macro-cell roamclose to a HeNB, the uplink of the HeNB can be severely interfered withparticularly when the HeNB is far away (for example >400 m) from themacro-cell, thereby, degrading the quality of service of UEs connectedto the HeNB. Currently, the existing Rel-8 UE measurement framework canbe made use of identify the situation when this interference might occurand the network can handover the UE to an inter-frequency carrier whichis not shared between macro-cells and HeNBs to mitigate this problem.However, there might not be any such carriers available in certainnetworks to handover the UE to. Further, as the penetration of HeNBsincreases, being able to efficiently operate HeNBs on the entireavailable spectrum might be desirable from a cost perspective.

The various aspects, features and advantages of the disclosure willbecome more fully apparent to those having ordinary skill in the artupon careful consideration of the following Detailed Description thereofwith the accompanying drawings described below. The drawings may havebeen simplified for clarity and are not necessarily drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, where like reference numerals refer toidentical or functionally similar elements throughout the separate viewsand which together with the detailed description below are incorporatedin and form part of the specification, serve to further illustratevarious embodiments and to explain various principles and advantages allin accordance with the one or more embodiments of the present invention.

FIG. 1 a is a heterogenous deployment with a MNB and HeNB and thedownlink subframe configuration of the carrier transmitted by the MNBand HeNB.

FIG. 1 b shows more details about the uplink and downlink subframestructure.

FIG. 2 illustrates the method of shifting HeNB subframes by k=2 symbolsrelative to macro-cell subframes.

FIG. 3 illustrates the method of shifting HeNB subframe by k=16 symbolsrelative to macro-cell.

FIG. 4 illustrates an exemplary subcarrier structure of 5 MHz and 15 MHzcarriers with raster frequencies separated by multiple of 300 kHz.

FIG. 5 illustrates an exemplary subcarrier structure of 5 and 15 MHz DLcarriers.

FIG. 6 illustrates a process for receiving control messages whose DCIformat sizes are based on the first and second bandwidths.

DETAILED DESCRIPTION

In a heterogeneous network comprising macro cells and HeNBs cells thathave overlapping BW deployments, certain interference problems canarise. One such interference problem is one where the uplink (UL)transmission from a UE connected to a macro-eNB (MeNB) that is close to(i.e., within signal range of a HeNB) interferes with the UL of a UEconnected to the HeNB. This case has been identified as interferencescenario 3 in 3GPP TR 25.967 “Home Node B Radio Frequency (RF)Requirements (FDD) (Release 9)” in Universal Terrestrial Radio Access(UTRA) network.

The severity of the problem can be high when the separation between MeNBand the HeNB is large. This is illustrated by some simple calculationsas follows. The pathloss (PL) equation for typical macro-cellularenvironments (from TR 25.814) used in system evaluations is given by PL(dBm)=128.1+37.6 log₁₀(R), where R is in kilometers, for 2 GHz carrierfrequency. The MUE sets its UL transmit power based on the receiver SINRrequirement at the MeNB that is further dependent on the desired PUSCHMCS. From TS 36.213, the UL power control equation can be approximatedas P_(Tx,MUE)=max{P_(CMAX), I_(MeNB)+SNR_(req,MeNB)+PL_(MeNB-MUE)},where P_(CMAX) is the maximum allowed MUE transmit power per powerclass, I_(MeNB) is the co-channel interference at the MeNB receiver,SNR_(req,MeNB) is the required SINR for MUE UL transmission to supportthe desired MCS level and PL_(MeNB-MUE) is the patloss from the MeNB tothe MUE.

Table 1 summarizes the dependence on distance of PL and MUE transmitpower with P_(CMAX)=23 dBm, I_(MeNB)=−98 dBm and SNR_(req,MeNB)=10 dB.

TABLE 1 PL and MUE transmit power dependence on distance MeNB-MUEPL_(MeNB-ME) P_(Tx, MUE) distance (m) (dB) (dBm) 100 90.40 2.40 200101.72 13.72 300 108.34 20.34 400 113.04 23.00 500 116.68 23.00 600119.66 23.00 700 122.18 23.00 800 124.36 23.00 900 126.28 23.00 1000128.00 23.00

From these calculations, a MUE farther than 400 away from MeNB m startstransmitting at maximum power under the chosen conditions. For amacro-cell with 1 km cell radius, this means that roughly 80% of usersare transmitting at maximum power. Therefore, a MUE that roams close toa HeNB serving its users can severely degrade the UL throughput in theHeNB particularly when the MeNB-HeNB separation becomes large (>400 m).

Techniques such as adaptive uplink attenuation considered in theUTRA-framework 3GPP TR 25.967 are likely to be investigated in the LTEcontext for mitigating this problem. However, this alone might not besufficient in achieving the best spectral efficiency possible withheterogeneous deployments. Some methods that can be useful in makingHeNB deployments more efficient are discussed below.

A coarse geolocation of UEs is possible by thresholding either thepathloss (PL) of the UE from a HeNB or alternately by thresholding thedifferential pathloss between HeNB and MeNB. In one embodiment, if thePL (HeNB to UE) is below a pre-determined threshold, then the UE isclose HeNB. In an alternate embodiment, if the difference (PL(MeNB toUE)—PL(HeNB to UE)) exceeds a certain threshold, then the UE is not onlyclose to the HeNB, but it can pose a significant interference risk tothe UL of the HeNB. If a macro-cell UE that is far away from themacro-cell but near a CSG cell transmits with large power, it can causeUL interference to CSG UEs. For determining the pathloss from the HeNBto the UE, the UE can read the system information broadcast (SIB)containing information element pertaining to the downlink transmit powerof the HeNB. Alternately, it can make some assumptions on the downlinktransmit power (e.g., set it to maximum allowed power per the powerclass of HeNBs deployed in the network).

Several embodiments are described below for ensuring reliable HeNBdownlink control when the Home eNode B is close to a macro-cell eNB(MNB) if they are time aligned. Some embodiments rely on a Rel-9 UEshaving additional functionality that is similar to a simplified versionof carrier aggregation (sub-20 MHz and contiguous) although this featurewould more likely be deployed in LTE Release-9. In this case, separatecontrol channel support is needed so that the PDCH in a carrier canschedule resources in a bandwidth that exceeds the PDCCH transmissionbandwidth. In another embodiment, HeNB control regions are time-shiftedrelative to the macro-cell's control region and the macro-cellattenuates or mutes symbol portions that overlap it. Similarly themacro-cell can attenuate RBs that align with the HeNB's time-shifted SCHand PBCH. Carrier aggregation is not necessarily needed in this lattercase.

Unlike data (PDSCH, PUSCH), there is no HARQ for control channeltransmissions which must typically target fairly low BLER of 1% or less.Low transmission power HeNBs in proximity of high power Macro-cells willnot have reliable downlink control channels (e.g., PDCCH, PHICH, PCFICH,PBCH, SSCH). One way to solve this is to segment the LTE carrier andallow the MNB and HeNB to transmit their control signaling in separatefrequency domain resources. For example, if the LTE carrier is 20 MHzthen it would be segmented into 5 MHz and 15 MHz carriers on thedownlink with the MNB transmitting its control signaling (PDCCH, PHICH,PCFICH, P-SCH, S-SCH, PBCH) on the 15 MHz carrier and the HeNBtransmitting its control signaling on the 5 MHz carrier (see FIG. 1 aand FIG. 1 b). Carrier segmentation would avoid any downlink controlchannel reliability problems.

In one embodiment, both LTE Rel-8 and Rel-9 UEs would access the MNB asa 15 MHz carrier and receive control and broadcast signaling from MNBwithin 15 MHz. In this embodiment, however, Rel-9 UEs may beadditionally be assigned PDSCH resource on the remaining 5 MHz frequencyresources using DCI types corresponding to 20 MHz. For HeNB, both Rel-8and Rel-9 UEs would access the HeNB as a 5 MHz carrier while Rel-9 UEscan additionally be assigned PDSCH resources on the remaining 15 MHzfrequency resource using DCI types corresponding to 20 MHz. In thisembodiment, Rel-8 UEs would be limited to allocations of 25 RBs (whenattached to HeNB) or 75 RBs (when attached to MNB). Rel-9 UEs could beassigned any portion of the 100 RBs (when attached to either the MNB orHeNB).

In this embodiment, Rel-9 UEs would be signaled by higher layers onwhether to monitor normal DL DCI types corresponding to the DL carrierbandwidth (25 RBs if attached to a 5 MHz carrier or 75 RBs if attachedto a 15 MHz carrier) or to monitor wideband DL DCI types correspondingto 20 MHz with 100 RBs. Although the wideband DL DCI types correspond to20 MHz resource allocations, they are still signaled on PDCCH spanningthe nominal carrier bandwidth (i.e. 5 or 15 MHz) of the carrier that theRel-9 UE is attached to. Further, reception of wideband DL DCI's can berestricted to the UE specific search spaces. Rel-9 UEs can stillcontinue to receive normal DCI types in the common search space forPDCCHs that signal broadcast messages. The common and UE specific searchspaces are defined in 3GPP TS 36.213.

In another embodiment, for the uplink, both Rel-8 and Rel-9 UEs wouldmonitor UL DCI types corresponding to 20 MHz carrier bandwidth at bothHeNB and MNB. Uplink control signaling reliability can be maintained byusing PUCCH offset (so called “PUCCH over-provisioning”) for orthogonalPUCCH assignments between the HeNB and MNB carriers. Since the ULresources are not segmented, UL resource grants can be signaled to bothRel-8 and Rel-9 UEs using 20 MHz DCI types. This requires that Rel-8devices be tested to ensure they are capable of handling asymmetric DLand UL bandwidths (in this example, DL=5/15 MHz and UL=20 MHz). The DL(dl-Bandwidth) and UL (ul-Bandwidth) system bandwidths are signaled onMIB and SIB-2 respectively (see TS 36.331). Rel-8 device would also havefrequency offset between its DL and UL center frequencies. A PBCH andSCH occur in the center of each carrier as defined in Rel-8.

In one embodiment, the DL bandwidth parameter (dl-bandwidth) signaled inthe MIB corresponds to the bandwidth on which Rel-8 UEs can be assigneddownlink resources. Information regarding the wider bandwidth over whichRel-9 UEs can expect resource assignments can be signaled via the P-BCH(Physical-Broadcast Channel) by utilizing the reserved fields in the MIB(Master Information Block). This enables Rel-9 UEs to configure theirreceiver for wideband reception (i.e., 20 MHz reception) immediatelyafter receiving the P-BCH.

In another embodiment, information about the wider bandwidth can besignaled to the Rel-9 UEs using other broadcast messages, e.g., SIBs(System Information Blocks) or by using dedicated RRC (Redio ResourceConfiguration) messages. In this case, Rel-8 UEs should initiallyconfigure their receiver according to the dl-bandwidth parametersignaled in the MIB, i.e., same bandwidth as Rel-8 UEs (e.g., 5 MHz or15 MHz) and then later reconfigure the receiver to receiver widerbandwidth transmissions (e.g., 20 MHz) after receiving the appropriatebroadcast or RRC message from the base station.

In one embodiment, it is assumed the subframe time-alignment betweenmacro-cell and HeNB/Femto/Relay exists. In this embodiment, signaling issupported in Rel-9 to indicate BW of DCI format types to enable resourceassignment signaling of up to 20 MHz on a PDCCH that spans a smallerbandwidth (e.g., only 5 MHz or 15 MHz). Alternatively, in anotherembodiment, a separate PDCCH on one carrier is allowed to indicateresource allocations on a frequency segment attached to the carrier withcontrol signaling (e.g. 5 MHz carrier PDCCH indicates allocations in 15MHz frequency segment).

Another embodiment uses a PUCCH symmetrical offset (so called “PUCCHover-provisioning”) to maintain orthogonal PUCCH assignments when uplinkcarriers overlap (e.g., both UL carriers are 20 MHz).

Another embodiment is based on time shifting of HeNB transmission by ksymbols (i.e., to avoid overlap with MNB control region size k) and usesMNB power reduction or muting on the portion of a symbol (or symbols)that overlap the control region of HeNB (see FIG. 2). The MNB could alsouse power reduction on all the RBs (i.e., the 25 RBs) overlapping theHeNB control region to improve PDSCH performance for HeNBs very close tothe MNB. A single OFDM symbol HeNB control region (n=1) is preferred forPDSCH efficiency which leaves 5 CCEs for HeNB control channels whichshould be sufficient for HeNB control signaling. Due to the time shiftof HeNB transmissions, the last k symbols of the HeNB PDSCH region wouldsee interference from the macro-cell control region. The HeNB PDSCHoverlap with macro-cell control region could be accounted for by either(a) doing nothing and use all non-control symbols for PDSCH, (b) usetruncation so only 14-n-k symbols would be used for HeNB PDSCH or (c)still use 14-n symbols but account for overlap via MCS selection. Sincethe interference from the MNB carrier on the HeNB PDCCH signals (controlregion) is being avoided by time shifting the MNB carrier need not besegmented. The HeNB carrier can still be segmented.

Carrier segmentation for HeNB can be also avoided (as shown in FIG. 3)by allocating HeNB the full 20 MHz band as well but then an additionalsingle subframe shift (k=16 total symbols) is needed so its SCH/PBCH donot overlap the macro-cell's. Then the macro-cell would mute orattenuate its PDSCH symbol(s) overlapping the HeNB control region andwould also attenuate/mute RBs that overlap HeNB's PBCH/SCH. RRMmeasurements of HeNB are conducted as normal.

Table 2 below summarizes the different control reliability techniquesbeing considered in this paper.

In this embodiment, it is assumed that the HeNB is time aligned withmacro-cell. Shift HeNB downlink subframe by k symbols relative tomacro-cell downlink subframe so no overlap in their control regions.Macro-cell attenuates or mutes symbol(s) in its PDSCH region thatoverlap the HeNB control region. Macro-cell attenuates or mutes PRBs inPDSCH region that overlap SCH or PBCH.

TABLE 2 Control Reliability Techniques for Homogeneous Deployments HeNBMNB Time Grant Rsrc UL/DL Fixed HeNB Orthog. Orthog. Control ReliabilityTechniques BW BW Carrier Shift Allocation Center Freq HeNB & MNB ControlPBCH for Homogeneous Deployments DL UL DL UL Agg. (sym) BW signaledaligned CR size Coord. Region & SCH Alt1 - Carrier segmentation 5 20 1520 yes  0 yes no no no yes* yes** Alt2a - Carrier Overlap w. symbolshifting 5 20 20 20 yes n yes no (HeNB) 1 yes yes*** yes** Alt2b -Carrier Overlap w. symbol shifting 20 20 20 20 no 14 + n no yes 1 yesyes*** yes^(IV) Alt3 - Carrier Overlap w. subframe shifting 20 20 20 20no 14 no yes 3 yes no^(III) yes^(IV) n - is size of MNB control region(preferably n < 3) *if carrier aggregation then symbol muting isrequired for maintaining HeNB control region orthogonality **if carrieraggregation then MNB does not allocate RBs overlapping HeNB's PBCH/SCH***Muting by MNB for symbol portions of PDSCH RBs overlapping HeNBcontrol region ^(III)relies on PDCCH repetition assuming fixed controlregion size of 3 symbols (preferably also for MNB) ^(IV)MNB should notschedule RBs overlapping HeNB's PBCH/SCH -- this requires coordination

In another embodiment, time shifting to avoid control alignment betweenthe MNB and HeNB is not done. Instead, the HeNB repeats each PDCCH inits control region (or uses extra CCEs) and always uses the largestPCFICH (e.g., n=3) which could be signaled to Rel-9 UEs via SIB. If HeNBhas same bandwidth as MNB then full subframe shift (k=14) is needed sothat HeNB transmissions of PBCH and SCH do not overlap with MNBtransmissions of its PBCH and SCH. Additionally, the MNB can attenuateor mute PDSCH RBs that overlap with HeNB's PBCH/SCH. The MNB can alsoattenuate or mute the transmissions in some portions of its controlregion. Alternatively, a set of MNB CCEs can be blocked from use toreduce interference on a relatively small number of HeNB CCEs (n=1 HeNBcontrol region size is then possible). The small number of CCEs shouldbe adequate for HeNB scheduling (See Annex A for more details).

In one embodiment, carriers are overlapped and the system relies onPDCCH repetition or increased #CCEs/PDCCH to sustain PDCCH coverage. Theembodiment uses 1 subframe shift so PBCH and SCH of HeNB do not overlapwith MNB's. MNB can attenuate/mute RBs that overlap HeNB's PBCH/SCH aswell as portions of its control region.

In another embodiment, a set of MNB CCEs can be blocked from use thatwould reduce interference on a relatively small number of HeNB CCEs (n=1HeNB control region size is then possible). It is assumed a small numberof CCEs should be adequate for HeNB scheduling.

If it were possible to choose HeNB PCIDs then a PCID might be chosen soCCE REG locations of the HeNB were as close as possible to those of theMNB. Then separate CCE groups could be defined with one group allocatedto the HeNB and the other to the MNB thus reducing interference to HeNBCCEs. Instead a small number of CCEs (e.g., 5 CCEs which is the numberof available CCEs in the 5 MHz carrier case for control region size of 1OFDM symbol (n=1) given 2 or more TX antennas) can be chosen for theHeNB with REG locations that are closely aligned with REG locations of aset of CCEs in the MNB such that the set of CCEs (which can be largerthan 5) are not used or seldom used by the MNB (i.e., CCEs are in theMNB's blocked CCE set). In this case, it is not necessary to pick aspecific HeNB PCID but the HeNB would need to know the MNB PCID so itcould use it and its own PCID to determine the MNB's blocked CCE setwhich it would then signal to the MNB. The HeNB would also know whichCCEs it could allocate (in this case all 5 CCEs would all be in itsHNB's CCE Allocation set). In this case, the 5 CCEs of the HNB's CCEallocation set span the HeNB's common and UE specific search spaces. Ifnot (e.g., n>1 and/or BW>5 MHz) then some CCEs (e.g., 4) in the HeNBcommon search space and some (e.g., 4) in the HeNB's UE specific searchspaces would be selected for its HNB CCE allocation set and based onthese the MNB blocked CCE set would be determined. Based on theirrespective CCE sets the HeNB and MNB would not assign certain UEIDs totheir respective served UE's if they would cause hashing to blocked CCEs(or in the case of the HeNB map to CCEs not in the HNB CCE allocationset). The number of blocked UEIDs would be much smaller for the MNBgiven its control region is 3 OFDM symbols (n=3).

In another embodiment, common reference symbols (CRSs) for theMacro-cell and HeNB can be configured to use different CRS frequencyshifts to avoid full alignment which may help with HeNB channelestimation. Note that choosing guard band(s) appropriately throughselection of raster frequencies is another way to shift the Common RSsof the different bands to control the degree of overlap (see FIG. 5). IfHeNB and Macro-cell are not subframe time aligned then CRS overlap doesnot need to be addressed. Rel-9 UE served by the HeNB can rate matcharound the Macro-cell CRS RE locations.

In this embodiment, reference symbols are shifted using an existing PCIDmethod and/or by selection of carrier raster frequencies to improvechannel estimation of HeNB/Femto/Relay transmissions. Power boosting ofCRS also possible.

DC subcarriers of the MNB DL carrier (15 MHz for Rel-8) and the HeNB DLcarrier (5 MHz for Rel-8) should be on the 100 kHz raster locations sothey are accessible to Rel-8 UEs (e.g., see FIG. 4). Rel-9 UEs wouldstill only require a single FFT to demodulate transmissions for resourceallocations spanning 20 MHz by shifting their center frequency to afrequency corresponding to 20 MHz. For example, in FIG. 5 the Rel-9 UEwould first camp on 5 MHz or 15 MHz raster then shift its centerfrequency to the 20 MHz carrier raster frequency. FIG. 5 also shows twopossible raster selections for the 5 and 15 MHz carriers. One rasterselection results in 1 subcarrier overlap for the 5 and 15 MHz carriersand the other results in a guard interval of 59 subcarriers which wouldtend to mitigate any adjacent carrier interference (ACI).

In another embodiment, the guard band between 5 and 15 MHz carrier iseliminated (1 subcarrier overlap due to extra DC) so 20 MHz band used byRel-9 UEs completely includes 5 and 15 MHz carrier RBs. Adjacent carrierinterference (ACI) is higher in this case compared to using a guard band(e.g., 59 subcarrier guard band). ACI mitigation is lost if the guardband is cannibalized for more RBs for Rel-9 UE allocations.

While the present disclosure and the best modes thereof have beendescribed in a manner establishing possession and enabling those ofordinary skill to make and use the same, it will be understood andappreciated that there are equivalents to the exemplary embodimentsdisclosed herein and that modifications and variations may be madethereto without departing from the scope and spirit of the inventions,which are to be limited not by the exemplary embodiments but by theappended claims.

1. A method in a wireless device, the method comprising: receiving, atthe device, control signaling from a wireless base station in a controlregion of a downlink carrier, the control region spanning a firstbandwidth; receiving, at the device, a signaling message from the basestation indicating a second bandwidth; receiving, at the device, a firstcontrol message within the control region using a first Downlink ControlInformation (DCI) format size, the first DCI format size based on thefirst bandwidth; receiving, at the device, a second control messagewithin the control region using a second DCI format size, the second DCIformat size based on the second bandwidth, wherein the second bandwidthis distinct from the first bandwidth and the first and second controlmessages indicate downlink resource assignments for the downlinkcarrier.
 2. The method of claim 1, wherein the signaling message fromthe base station is a broadcast message.
 3. The method on claim 1,wherein the signaling message from the base station is a dedicated RadioResource Configuration (RRC) message.
 4. The method of claim 1, thefirst control message is a broadcast message and the second controlmessage is a dedicated message addressed to the wireless device.
 5. Themethod of claim 1, the first control message is received in a commonsearch space within the control region, the second control message isreceived within a wireless device specific search space within thecontrol region, wherein the wireless device specific search space isbased on a wireless device specific identifier.
 6. The method of claim1, wherein the first control message is a Physical Downlink ControlChannel (PDCCH) message and the second control message is PDCCH message.7. The method of claim 1, wherein the first bandwidth and secondbandwidth share at least one subcarrier.
 8. The method of claim 1wherein, the device is configured to receive signals on the firstbandwidth and second bandwidth.
 9. The method of claim 1, wherein thesecond bandwidth includes the first bandwidth.
 10. The method of claim 1wherein the wireless device has one 20 MHz receiver.
 11. The method ofclaim 1, wherein the first control message and the second controlmessage are received in the same sub-frame.
 12. A method in a firstwireless base station, the method comprising: receiving a signal from asecond wireless base station; determining a first set of control channelelements (CCEs) based on the received signal; transmitting controlsignaling on a second set of control channel elements, the second set ofcontrol channel elements distinct from the first set of control channelelements.
 13. The method of claim 12, wherein receiving a signal meansreceiving a signal containing at least a PCID of the second wirelessbase station.
 14. The method of claim 12, wherein receiving a signalincludes receiving a signal containing a set of CCEs that the secondwireless base station either does or does not transmit on.
 15. Themethod of claim 12, wherein the receiving a signal includes receivinginformation via a system or master information block transmission. 16.The method of claim 14, wherein receiving a signal includes receivinginformation via a RRC transmission.
 17. The method of claim 12, whereinreceiving a signal includes the first wireless base station takingenergy measurements on the CCEs and/or REGs in the control region of thesecond wireless base station.
 18. The method of claim 12, whereindetermining a first set of control channel elements based on thereceived signal includes determining which set of CCEs and/or REGs thesecond base station transmitted on.
 19. The method of claim 12, whereindetermining includes determining the CCE and/or REG power levels used bythe second base station in its control region.
 20. The method of claim12, wherein determining a first set of control channel elements based onthe received signal includes determining a subset of user equipment IDs(UEIDs) for the first base station from the total UEIDs available foruse by the first base station that are allowed to be assigned to userequipment (UE).
 21. The method of claim 12, wherein the second set ofcontrol channel elements is distinct from the first set of controlchannel elements means that the second set of control channel elementshas less than 50% overlap with the first set of control channel elementsin terms of time and frequency allocation.
 22. A method in a firstwireless base station, the method comprising: receiving a first signalfrom a second wireless base station; determining a first Physical UplinkControl Channel (PUCCH) offset based on the received first signal;transmitting a second signal indicating a second PUCCH offset, thesecond PUCCH offset distinct from the first PUCCH offset.
 23. The methodof claim 22, wherein the first signal received from the second wirelessbase station is a system information broadcast message indicating thefirst PUCCH offset.
 24. The method of claim 22, wherein the secondsignal indicating the second PUCCH offset is a system informationbroadcast message transmitted by the first base station.